Time base sweep and intensifier pulse generator



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J. M. LESTER TIME BASE SWEEP ANDjINTENSIFIER PULSE GENERATOR Filed arch 25, 1943 Patented f 7, 194g UNiTED STATES TENT OFFICE Delaware Application March 25, 1943, Serial No.`480,570 irciaims. (ci. 3154-22) My invention relates to` circuits` and methods for generating time base sweeps and intensifier pulses as applied to cathode raytube indication.

In one application of cathode raytubeindication a wave form is projectedon the tube screen for analysis as a functioniof time. Here thespot must sweep, across the screen at a uniform Velocity so that the` deiiection of the beam at any instant is proportional to the time elapsed since the beginning of the sweep.`

To produce this effect, `namely that of the sweep, it is necessary to apply to the deiiecting plates of the cathode ray tube a voltage that increases linearly with time up to a maximum value and then falls abruptlylto datum; For this purpose a voltage having a sawtooth wave form has been found to be satisfactory with certain exceptions, which as concerns the examinations of sinusoidally varying phenomena, may be described as follows. i l v Since the fall in voltage at the end of the linear rise of the sweep portion of this wave con sumesa part of the cycle, thereturn of the spot or electron beam is not instantaneous, and a section of the wave under study is traced during ray tube indication, namely, radar range measurement, the problem of retrace `or flyback presents itself in a slightly different manner.`

v Here, the sweep wave may be impressd upon one set of the tubes deiiecting plates, and a pulse, reflected from a target, received on the other deflecting plates. For example, the sweep wavemay be applied to the horizontal delecting plates, in which case the tube screen will be graduated horizontally from zero to maximum range, and the reflected signal received on the Vertical deecting plates. Withthe tube connected thus, the linear portion of the sweep wave will` cause the electron beam to sweep` from zero to maximum range, and the reflected signal will appear at some point between, indicative of the distance from the target. At the endof the sweep, however, the electron beam, is deiiected back `to zero, due to characteristics of `the sweep waveV discussed above, and a portion of the signal pattern may be retraced.

Similarly, where the sweep is applied to the horizontal deflecting plates and the reflected signal is received on the grid of the tube, the eiTect of. retraceis likewise present. Here the electron beam is continuously swept from zero to maximum range by the sweep wave, and the reflected'signal appears as a spot at some point between to indicate the target range. Since the beamv is deiiected horizontally by the sweep portion of theY sweep wave and returned by its abrupt ,fallxto datum, it is evident that it is impossible for the observer to tell on which portion of the sweep the reected `signal is received, as long as the retracezsection of the pattern is present.

ln all instances then, it is necessary to eliminate the portion of the projected patternprcduced by that part of the sweep wave which consumes any portion of its cycle other than that in which the voltage is increasing or decreasing linearly ,with time. To effect this elimination, it is common practice to bias the grid of the cathode ray tube beyond cut-01T during the return sweep by the application of a pulse Voltage synchronized to give bias for only that portion of the sweep cycle during which the voltage is not varyinglinearly with time.V

Many methods have been devised for generating this intensier pulse, among them bein g the multivibrator circuit, which has been used `rather extensively in range measurement indication. In this particular application, how ever,it isY often desirable to change the range indication and at the same time utilize the full scale deection of the cathode ray tube, which change makes the use of a multivibrator circuit for intensifier lpulse generation less practicable. Y For example, at a given frequency, the full scale deflection of a tube may be graduated for a range of fifteen miles. It may then be desirable, at the will of the observer, to reduce the range indication to seven and one-half miles for the same full scale deflection, and in such case the form` of thesweep wave must necessarily Abe changed.

`This may be illustrated by a description `of actual sweep wave forms for lthe condition stated. To give a range of fifteen miles, the sweep wave may be of the inverted sawtooth form, i. e., having an abrupt rise, lineal decrease with timey to datum, abrupt rise, lineal decrease, etc.; while for a range of seven and one-half miles the form wouldbe abrupt rise, lineal decrease with time to datum, horizontal displacement, abrupt rise, lineal decrease, horizontal Adisplacement,jetc. Thus, such a decrease in range necessitates a change. in theform of the sweepywave which increases its slope and extends theretrace portion of the pattern to include that section of it produced by the segment of the sweep wave described above as horizontal displacement and abrupt rise. To eliminate this retrace, it is readily seen from the above that the grid of the cathode ray tube must be biased by an intensifier pulse having a particular wave form and being synchronized to render ineffectual that part of the sweep described as horizontal displacement and abrupt rise. l

To produce such an intensier pulse .-with a multivibrator, it is necessary to change the cir.- cuit parameters for each change in the sweep wave; and, while this method proves satisfactory from the standpoint of erasing the retrace, it is less practicable in operation.

In the rst place, the intensifier `.pulse is `generated in a, circuit independently of the sweep, and a change of range indication therefore requires changes in two separate circuits. ondly, the multivibrator is, without elaborate renement, unstable, since .it needs a synchronizing pulse for its operation and therefore requires repeated adjustment.

Further,V with presentfintensierpulse `generating means it is not possible to change the frequency of the input wave, maintain a'xed sloped sweep wave, and at the same time vary the intensier pulse to synchronize it withithechanged sweep wave. This particular characteristic of present apparatus limits the .interchange of equipment lwhere inputs of different frequencies are used.

Accordingly, itis an object of my invention to provide a circuit for generating time base vsweeps g and intensifier pulses which with'a single adjustment for a change in the sweep Awave .will automatically produce an intensifier pulse, 'of proper wave form, synchronizedto .eliminate the retrace of the changed sweep wave.

lAnother object of my invention istoprovide a circuit having a characteristic described in the paragraph next above which will generate a sweep of constant slope irrespectiveof frequency changes in the input voltage.

It Ais also'an object of my invention tofarrange a circuit for generating intensierpulses which is stable in operation anduwhich doesnot require repeated adjustments.

Another object of my invention is to a circuit of unitary design which will .generatera variable sweep wave and an-intensier pulse simultaneously.

Another object of my invention is `toprovide-in a single circuit a kvariable sweep wave generating branch and an intensier pulse generating branch so arranged that the output of theformer branch' will be fed to the latter branch to produce a pulse which will change in form with any variation in the form of the sweep wave,

A further purpose of my invention is-to provide a method for generating an intensifier pulse from a sweep wave which it is to intensify,thatwill automatically maintain synchronism with the sweep as the latter is varied.

1n carrying out the objects of my invention, I have arranged in a preferred embodiment thereof, a single circuit comprising a sweep Wave generating branch and an intensierfpulse generating branch. A square wave of any desiredffrequency is impressed upon this circuit where, in the sweep generating branch,-it is differentiated, amplied and clipped to vform a sawtooth wave across a resistive-capacitive network. A portion of the output of this branch is taken from the Secprovide circuit for use as a sweep and a portion is also fed to the intensiiier pulse generating branch Where it is inverted, clipped and amplified to form an ntensier pulse.

A suitable electronic discharge device, acting as a constant current element, is employed as a discharge resistor .in the resistive-capacitive network lof thenalstage ofthe sweep generating branch. The value of the capacitive discharge current of the network is changed by varying a dropping resistor placed in the screen grid circuit .of :the ,constant current element which in turn changes the slope of the sawtooth wave and the Width ofthe intensifier pulse.

Selected values .of plate resistance together with the plate capacitance of the inverter stage in the .intensifier-pulse,generating branch provide suiicient delay in the resultant intensifier pulse so that it can be used without further alteration to intensify the sweep portion of the sawtooth wave. This holds .true Afor any form of sweep-wave generated, andsan intensier pulse is thus automatically generated which is synchronized with -the sweep :fromI Whichit lis obtained.

Fora more comprehensive understanding of my invention, reference lis made tothe yfollowing detailed` description `and thefaccompanying dra-wing in which- Fig. 1 is a circuit diagram of an embodiment of my invention;

Fig. 2A is a graphical representation of a sweep wave and its accompanying intensifier pulse for a given condition of range, asgenerated by the circuit shown in Fig. 1;

Fig. 2B is a similar representation of the waves shown in Fig, 2A when the range is reduced by one-half;

Fig. 3A is a graphical representation of a sweep wave and its accompanying intensifier pulse as generated by the circuit shown in Fig. l, for a given frequency;

Eig.. .3B is `a similar exhibition of the waves shwniniFigAaatfhalf ofzthe given frequency; an

Fig. Liis an enlarged View of one pulse taken from :thetcircuit atdl, Fig. 1, showing the effect of integration in .theintensier pulse generating branch.

i-In the circuitillustrated in Fig. 1, the -sweep wavegenerating branch .49 comprises the tubes 9, |1,,andf22, and the -intensier pulse generating .branch 50, the -tubes 33 and di. The wave forms produced 'at Various points within each y branchare represented by segments thereof.

In thesweep generating circuit thefgrid 4 of tubeg, .whichmay be vor 'the triodetype, vis connected to the input terminal i, through' the differentiating-.coupling:elements 2 and-'3. The anode of this tubeis .connected-to positive energy source', throughithe plate resistor and its cathode .S is yconnected directly to ground.

,The output of tube 9.s fed :to lthe grid l5] of tube `lvll,"illustrated asaitriode, through the condenser Iland the coupling elements l5 and it.

t Plate i8 is connected .to positive energy source k8 andcathode'vflfto terminal point l5 intermediate the-resistor `I5 and the capacitor i6. A tube y22 isconnected in the cathode circuit of tube'i'i and acts as a-.capacitordischarge resistor. The plate 23 of tube 22 and the cathode 20 of tube l1 are tied together; and the vcathode 27, con-trol grid 26 (through a resistor), and suppressor 24 of tube 22 are grounded as shown. Ihe screen grid 25 is byrpassedto'the cathode `2l by capacitor 29 and is connected to source 8 Athrough rheostat 3|.

The output of tli'e sweep generating branch is taken from "thecathode T of tube I1 and delivered to the terminal from which pointit isfed to the initial stage 33 oftheintensier pulse generating branch 5U, and. also transmitted as a sweep-wave to'apair `of deectingplates of the oscilloscope 5I.

From the'terminal 30 the cathode output of tube I1 is received by grid 35 of tube 33 through the coupling elements 53 and 54. Anode 34 of tube 33, the plate capacitance of which is represented by the phantom capacitor 38, `is connected to `positive source through the plate resistor 32, and cathode36 of tube 33 is connected to ground through resistor 31. `The plate resistor 32 together with the plate capacitance 330i tube 33 constitutes "an integrating circuit, i the function of which will be explained later.

The output `of tube 33 is in turn fed to the grid42 of triode 4l, whichlis coupled for grid leak bias, through the capacitor 39 and resistor t3. Anode 44 is maintained positive by the energy source viithrough the plate resistor `t5, and the cathode 4G is connecteddirectly to ground. Connected in parallel across `the anode and cathode leads of tube 4I is a capacitor 48 which,

cuit with reference to one of its applications and its operation can best be visualized by referring to Figures 2A, 2B, 3A and 3B, where in all instances the useful portion of the sweep wave is emphasized in the illustration` as a heavy black line.

Let it be assumed that for a given range indiv cation a sweep wave, such as 55, Fig. 2A, is employed to give full range deflection on the tube screen of a cathode ray tube indicator. Such a wave would necessarily have a sweep portion 5l] having a denite slope which `must be intensified to prevent the 'effect of retrace. To do this, the portion 51.`of the sweep wave is erased-by biasing the grid ofthe cathode ray tube"with an intensifier pulse having the wave form 58.

Now, if the range is to be reduced by one-half and the same fullscale deflection used, the time necessary for full sweep must also bereduced by one-half, and the slope of the `sweep must be doubled.

To meet these requirements a sweep wave 6D, Fig. 2B, is used having a sweep portion 6I, the slope of which is equalto 2S.` Here again the retrace portion G2 of` the wave must ybe erased,

and for this purpose `an intensifier pulse having a wave form 63 is used.

If the range is to be reducedto one-fourth, three-fourths, or to any other fraction, changes in the slope of the sweep must be made with ac: companying changes in the intensifier puls which are similar to those illustrated.

In generating the required sweep wave and its accompanying synchronized intensifier pulse for each given condition of` range indication, the operationofwthe circuit diagrammed inFig. 1 is 50. sawtooth wave or a modification thereof is in- A square wave, impressed upon the input terminals I of the circuit, is differentiated by the coupling elements 2 and 3 shown respectively as a variable capacitor and a xed resistor. The differentiated wave is next fed to the grid 4 of tube 9 in which stage it is clipped and amplified to appear as a positive pulse across the load resistor 1. This pulse is then received by the grid I9 of the electronic discharge device I1 from whose cathode 20a sawtooth wave, or a modication thereof, is obtained due to the charging action of capacitor I6 and the constant current element 22 which maintains the discharge of the capacitor at a constant rate.

Since the constant current element 22 controls the` discharge rate of the current `discharge device I6, the slope of the sweep taken from the cathode 20 of element I 1 is a function of the plate resistance of element 22. To effect variation in the slope of the sweep, it is therefore necessary to vary the discharge rate and accordingly the plate resistance of element 22.

For this purpose the variable resistor 3l is interposed in the screen grid circuit of element 22 to control the voltage applied to it, and changes in the slope of the sweep taken from terminal 3B are made possible by the following circuit operation.

As the resistance of rheostat 3i is decreased, the screen grid voltage of element 22 is increased with a resultant decrease in the plate resistance thereof. As the plate resistance of element 22 is decreased, the discharge rate of capacitor IS is increased and the slope of the sweep is in turn increased. Conversely, the slope of the sweep is` decreased with an increase in the resistance of rheostat 3|.

Since the intensifier pulse must be synchronized with the sweep which it is to intensify, the sweep wave itself is used to generate the pulse.

Thus, the cathode output of element I1 is fed to the grid of the electronic device 33 comprising the first stage of the intensifier pulse generator From the anode 34 of this device, where the peak is amplified as the intensifier pulse. Thisr portion 52 oi the wave is selected because of its proximity to the retrace portion of the sweep wave, thus requiring a minimum amount of delay in the circuit. Bias by grid leak is used, since the value thereof is a function of the amplitude oi the input wave and clipping action of the tube is maintained fairly constant.

The operation of elements 33 and 4l need not be treated in detail, since they perform wellknown functions with standard operation. The elect of certain parameters within the circuit, however, is of interest.

As stated previously, the load resistor 32 of tube 33 acts with the plate capacitance 33 of that element to provide an integrating stage for the pulse generating branch as does plate resistor d5 in conjunction with capacitor i8V connected acrossthe tube 44.l This portion of the circuit is necessary lto the successful .operation of zthe circuit, as willnow be shown.

`In Fig. 4 .there is shown an enlargementzgi of one pulse of the output .Wave form Ataken .from the circuit at termina?. 'iliFig 1. This-.wavehas superposed on it a pulse B5-which :wouldobtain if. the integrating elements were not present in the circuit. Comparison of these two Ypulses clearly shows that the value of the voltage neces.- sary to intensify the indication'on the cathode ray tube screen is reached at a time interval yt before the same voltage is reached y,ley pulseff. Translated into terms of effects, this means lthat when the pulse 66 .is used to intensify .the sweep taken from terminal 3l), intensification Loccurs prematurely by the time t and a -portion'of the retrace is intensified as well as the sweep.

Since the sole purpose of .the pulse is to era-se the retrace, it is evident that -thepulse 66 is not suitable and that proper intensier biasmustibe delayed until it is in synchronism with thecsweep portion of the sweep wave. 'Such is'the function of the integrating elements 32, 38, :t5 and t8, which change the shape of pulse 66 to that of pulse 65, their action being to attenuate-the high frequency components of the `wave `andpass the low frequency components.

in the discussion of the circuit operation'up to this point, reference has not been made to the effect oiinput frequencylchanges, and-it Lhas 'been assumed for-the conditions stated'that this -f-re' queney has been maintained constant.

lt is a desirable characteristie'oi the circuit, particularly in its application to range Imeasurement, that variations in thelinputi-requencyhave no appreciable effect on its operation. Illustrative of this fact are the output graphs shown yin Figs. 3A and 3B. For a given input frequency and a fixed setting of resistor 3|, thecircuit shownin Fig. l may deliver respectively at :the output terminals 3? and di thereof a sweep lwave 4'l5 (Fig. 3A) and its accompanying-intensier pulse i8. If the input frequency is then reduced Yby one-half, the resultant outputs will approach the respective wave forms 'it and 8,-Fi-g. 3B.

A comparison of the waves 'i5 and'r'i `shows that the sweep portion 'il of wave l5 is identical with portion 7i.; of wave i9 both as to slope and duration. This condition of equivalency is due to the fact that the slope of the sweep generated by the circuit in Fig. l is a function ofthe time rate of discharge of capacitor 16 which iscontrolled by the constant currenteiemont 22.' Since the rate of discharge of capacitorlS-is unaffected by frequency variations, it follows that for afixed setting of the rheostat 3l, the sweep characteristics of the wave `generated are'immune to changes in input frequency. Further, the'intensiler pulse as such remains unaffected since 'it is obtained from the sweep wave.

While a frequency change of onenhalf -is here used for illustration, it is .understood` .that the same condition holds .truevfor allfrequency variations wthin reasonable limits.

summarizing, a square wave is differentiated, clipped and amplied in branch 49, Fig. 1, toform a sweep which is unaffected by reasonable changes in input frequency. A portion of the output of this lbranch is then fed to the pulse generating branch 59 where it is inverted, clipped, amplied and integrated to form a pulse which is synchronized to occur in time relation Withthe retrace portion-of the sweep wave from which it is formed. Variations in the characteristics of the sweep are effected by a single adjustment of rheostat-3I which-'simultaneously efiects ohangeslinthe phase' of 'fthe intensifier .pulse :tog-synchronize itrwithathe altered sweep.

-Modications =of my invention .are i of. course possible ...and may suggest 1 :themselves from :the foregoing disclosure. ,The ..embodiments herein shown and described are to be considered,etherefore,. as -illustr.ative o nly, :andzithe lspiritrand scope of .myfinventon vare :to :be limited-solely by the appendedfclaims.

f L fln eombinationfaiinear .time .base sweep generating stage, .meansior furnishing a..dif ferentiated square-wave .-.to the input .oisaidsweep generating stage, ,f-means yior zeon-trolling ,said sweep .generating sstage gto. vary the'islope of n@the sweepiwave, and aninverterstage-.andfa clipping and amplifying stage 'connectedinascade'tozthe output` of said sweep `generating stage Y.toithereby form an intensiiier pulse awhiehis synchronized with'zthe Output ofisaid sweepgenerating stage.

2. In :a sweep-,wave :generating ci-recit, .a time base sweepigenrerating stage :hal/ing afconsta-n-t current control device; aninverftertstage for receiving the output of said sweep generating stagaand acli-ppng and ampliying stage coupled to said sweep generating stagefby means of; a delay circuit.

3. Ina sweep wavegeneratingcci-rcuit,.a :time base sweep generating stage havingaconstant currenteontrol-davicenandian invert-.er stage for receiving-apart .oftheoutput lof said sweep generating stage to produce an intensier pu1se,.said inverter stage vincluding :means :for i delaying the occurrence of .the effective lportion .of said iintensiier pulse l'with-respect totime.

4. Inr a variable sweep .-wave generatingcircuit, a sweep 4waive generatorand an .inverter stage coupled. thereto for producing an` intensifier pulse, said inverter stage including means for delaying the occurrence of .theieffective portion of said intensifier .pulse y.with respect tol time.

:5. fIn combination, a linear time :baseigenerating circuit, -an :.intensiedfpulse generati/ng and delaying circuit, means interconnecting said. linear time base generating circuit-and said intensifier pulse generating circuit, and means for changing the wave form of the linear time base, said lastmentioned means being operable through said interconnectingmeans to yproduce an accompany ingsynchronizing change f in the intensifier .pulse wave form.

.-6. `In acombination sweepwaveand intensiner pulse generating circuit, ,a ,differentiating input coupling, alinear .time basegenerating stage, an inverter stage-including :.a .delay circuit, .outputconnections interposed :between said linear time base generating circuit. and said inverter stage for delivering a sweep Wave, a clipping .and amplifying stage :for receivingstheoutput .of said inverter stage, -and'output connections: for delivering an intensifier pulsewave.

7. In a linear time base vgenerating circuit` means ior .generating tand .delaying a sweep wave, means for generating an intensier pulse, and means lfor;interconnecting said sweep-.wavel generating .circuitand'fsaidjrrtensier: pulse .generatingcircuit: whereby va change of slopelinzthe sweep Wave efectedby a changein .the constants of said sweep generatingcircuit automatically effects an accompanying change iin .the Iwave Iform vof the-intensier .pulsefto thereby synchronize it with thef'altered sweep-wave.

Y 8.v In combinationpa cathode-ray tubeindicating device, a Wave generating circuit comprising a sweep wave generating branch and an intensifier pulse generating and delaying branch for generating a sweep wave and an intensifier pulse, means for varying the wave form output of said sweep wave generating branch, and means interconnecting said sweep wave generating branch and said intensifier pulse generating branch whereby a change in the wave form output of the sweep wave generating branch automatically produces `a corresponding change in the intensifler pulse wave form which automatically synchronizes said intensifier pulse with the altered sweep wave.

9. In combination, a circuit comprising a sweep wave generating branch and an intensifier pulse generating branch, said sweep wave generating branch comprising differentiating means, means for clipping and amplifying the output of said differentiating means, a current discharge device and means for controlling the discharge of said current discharge device to deliver a time base sweep of variable slope; and said intensier pulse generating branch comprising inverting means, clipping and amplifying means, and integrating means, said inverting, clipping, and amplifying, and integrating means being operable to produce a pulse synchronized in time relationship with the sweep wave output of said sweep' wave generating branch.

10. The method of generating an intensifier pulse, comprising `the steps of differentiating, clipping and amplifying a square wave to produce a sawtooth wave, inverting said sawtooth wave, and clipping, amplifying, and integrating the same.

11. The method of simultaneously generating a variable sweep wave and an accompanying synchronized intensifier pulse, comprising the steps of differentiating, clipping and amplifying a square wave to produce a sawtooth wave, invert- 10 same, and controlling the time rate of discharge.

14. A method of generating an intensifier pulse from a sweep wave which it is intended to intensify comprising the steps of inverting the sweep wave, clipping the same, and delaying the occurrence of the effective portion of said intensifier pulse with respect to time.

15. A method of operating an oscilloscope which comprises the steps of supplying a sweep wave to a pair of deecting plates thereof, inverting and delaying the sweep wave to form an intensier pulse, and applying the intensifier pulse to the oscilloscope.

V16. An intensifier pulse generator comprising an inversion stage with input connection for receiving a sweep wave to be intensified, and delay means for delaying the occurrence of the effective portion of said intensifier pulse with respect to time.

17. A method of operating an oscilloscope which comprises the steps of supplying a sweep wave to a pair of deecting plates thereof, deriving an intensifier pulse from the sweep wave afterdelay thereof, and applying the intensifier pulse to an electrode of said oscilloscope.

JOHN M. LESTER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,933,219 Nakajima et al Oct. 31, 1933 2,052,183 Lewis et al Aug. 25, 1936 2,059,004 Leeds Oct. 27, 1936 2,078,644 Swedlund Apr. 27, 1937 2,114,938 Puckle Apr. 19, 1938 2,126,243 Busse et al Aug. 9, 1938 2,230,926 Bingley Feb. 4, 1941 2,241,256 Gould May6, 1941 2,284,714 Bedford June 2, 1942 2,303,924 Faudell Dec. 1, 1942 2,313,967 Read, Jr Mar. 16, 1943 2,355,363 Christaldi Aug. 8, 1944 2,405,238 Seeley Aug, 6, 1946 FOREIGN PATENTS Number Country Date 459,041 Great Britain Dec. 28, 1936 Certificate of Correction Patent No. 2,455,373. December 7, 1948. JOHN M. LESTER It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 8, line 44, claim 5, for the Word intensified read intensver; line 64, claim 7, strike out and delaying and insert the same after generating in line 65, same claim;

and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the case in the Patent Ofce.

Signed and sealed this 28th day of June, A. D. 1949.

[SEAL] THOMAS F. MURPHY,

Assistant ommsszoner o f Patents.

Certificate of Correction Patent No. 2,455,373. December 7, 1948. JOHN M. LESTER It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 8, line 44, claim 5, for the Word intensified read intensijer; line 64, claim 7, strike out and delaying and insert the same after generating in line 65, same claim;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oce.

Signed and sealed this 28th day of June, A. D. 1949.

[SEAL] THOMAS F. MURPHY,

Assistant ommz'sszoner of Patents. 

